Atmospheric pressure plasmas have been known since the dawn of man. A classic example is lightning. These atmospheric plasmas (DC-type) occur when a high potential causes the dielectric breakdown of air (&gt;8 KV/cm in air). This type of plasma is used for producing various types of ceramic coatings in an apparatus known in the industry as a "plasma gun". Most other plasma producing devices do so in a vacuum system. Such vacuum-based systems are widely used in the microelectronics industry both for the deposition of thin films and for various etching and surface modification applications. Most of these vacuum-based plasma generating systems use RF or microwave energy excitation to sustain a stable plasma environment. Whereas a stable plasma is relatively easy to generate and maintain at low pressures it is much harder to do so at ambient pressures, due to the very short mean free paths and large recombination rate of the plasma radicals. Discussions of vacuum-type plasmas are given in "Handbook of plasma processing technology", edited by S. Rossnagel, J. Cuomo, and W. Westwood.
Whereas the capabilities of vacuum-type plasmas are limited by the size of the vacuum chamber and the associated pumping system, an atmospheric pressure plasma system can be configured with very little limitation on the size and shape of the objects treated. It can be made compact and portable as described in our co-pending U.S. application Ser. No. 08/572,390 filed Dec. 14, 1995, details of which are incorporated herein by reference. This system can also be scaled up with very little additional cost either through a large parallel plate configuration or through an array of small orifices, it can be installed in a variety of environments without any facilitation needs and its operating costs and maintenance requirements are minimal.
Prior Art Publications
H. Koinuma et al., "Development and Application of a Microbeam Plasma Generator" Appl. Phys. Lett. vol. 60, p. 816-817, (1992) K. Inomata, "Open Air Deposition of SiO.sub.2 Film From a Cold Plasma Torch of Tetramethoxsilane-H.sub.2 -Ar System" Appl. Phys. Lett., vol. 64, p. 46-48 (1994)